Underactive Thyroid

One of the most common concerns for people with hypothyroidism (Underactive Thyroid) is maintaining proper body weight. For people with Hashimoto’s (the most common cause of hypothyroidism) this comes in 2 varieties. They gain weight and can’t lose it or they have trouble keeping it on.

The Thyroid Influences Metabolism One of the obvious things that people think about with hypothyroidism and weight gain is the fact that the thyroid has an impact on the body’s metabolic rate. In technical terms, metabolism is the amount of oxygen used by the body over a amount of time. When this measurement is made at rest, it is called the basal metabolic rate or BMR.

High or low BMRs are associated with changes in energy balance. Energy balance comes down to the difference between how many calories one eats and how many calories one’s body burns.

Things that create a high BMR, like amphetamines, for example, often cause a negative energy balance which results in weight loss. (This is one reason why you tend not to see many overweight speed freaks.) Based on this, many people originally assumed that changes in thyroid hormone levels lead to changes in BMR and the same weight losses. Unfortunately, it’s a little more complicated than that.

Other hormones, proteins and neurotransmitters have also been found to be part of the mix and these all also have influence on energy, food intake and body weight.

Leptin The Body’s Fat Programmer Leptin is a hormone that is made in your fat cells and it is involved in maintaining body weight and has influence on the thyroid. Leptin acts as an important control system that communicates to other organs about the state of your fat balance and whether to eat more or stay in low-metabolism survival state. When you have more fat cells, you get higher leptin levels. The high leptin lets your hypothalamus (a kind of master endocrine gland in your brain) know that you don’t need to eat as much. Your metabolism slows (and this signals you to make more Thyrotropin-releasing hormone (TRH), and this raises Thyroid Stimulating Hormone (TSH) and the TSH tells your thyroid to make more thyroid hormone. This is what happens when everything is working properly. But with hypothyroidism, lots of things are often not working properly and many people develop leptin resistance causing people to become overweight as they use less energy.

Dieting Can Make This All Worse

Leptin resistance makes the hypothalamus believe that you are in starvation mode, and you make more fat, and slow down thyroid hormone production. Your appetite increases, you become insulin resistance and fat breakdown slows down.

Over time, you gain weight, especially around the mid-section, and it becomes more difficult to lose the weight and accumulated fat.